I have an Asus motherboard with similar onboard NIC device
Onboard NIC would work probably better if driver r8168 was used instead of r8169
The driver can be installed using this command
sudo mhwd --install pci network-r8168
Or use Manjaro Settings Manager > Hardware Configuration GUI:
Various issues with Manjaro KDE
suggest you change to r8168 driver with Manjaro Settings Manager
manjaro-settings-manager -m msm_mhwd
enable option in bottom left corner - Show All Devices
Look in section Network controller > RTL8111/8168/8411 for
network-r8168
Right click on
network-r8168
and select Install
Manjaro Settings Manager will install the driver for all installed kernel versions and create a blacklist command to prevent driver r8169 from loading